1. Field of the Invention
This invention relates generally to static charge eliminators, and more particularly to a grounded grid static discharge apparatus for dissipating static charge on moving sheets.
2. Description of the Prior Art
In order to improve the productivity of high speed copier/duplicators, apparatus has been described in Belgian Pat. No. 835,568 issued May 13, 1976, for recirculating discrete pages of an original multi-page document to enable the document to be copied in page sequential order. This apparatus, called a recirculating document feeder, removes discrete pages of the original document from a hopper, feeds the pages seriatim to the platen of an electrophotographic copier and, after exposure to an illumination source for obtaining an image of the document page, returns the page to the hopper. The transport of the pages about the recirculation path is accomplished by an oscillating vacuum feeder and by friction feed rollers.
As is well known, due to the phenomenon referred to as the triboelectric effect, when two members are moved relative to one another, friction contact between the surfaces of the members generates a static electric charge on the surfaces. Thus in a sheet transport apparatus, such as the recirculating feeder, as sheets (discrete document pages) slide across the glass platen (or any other support surface), or move relative to one another in the sheet stack, static electrical charges may build up on the sheets. When the sheets develop such a charge they tend to be attracted to (or repelled from) adjacent surfaces with which they come in contact rather than to slide readily over such surfaces. This reaction between the sheets and the opposed surfaces may interfere with the feeding of the sheets and can result in jams in the transport apparatus.
Many different means have been employed to eliminate the static electrical charge on moving sheets in a transport apparatus. One effective mechanism for removing the static charge includes an electrical conductor positioned adjacent to the sheet travel path, as described in U.S. Pat. No. 983,536 to Chapman, issued Feb. 7, 1911. The conductor is connected to a high voltage alternating current source which creates an electrical field of alternating polarity surrounding the conductor. A second conductor, which is grounded, is positioned between the high voltage conductor and the sheet travel path. The grounded conductor normally absorbs the ions of the electrical field of the high voltage conductor. However, when sheets having a static charge move into the vicinity of the grounded conductor, the grounded conductor permits passage to the sheets of a proportional number of ions of opposite polarity to the charge on the sheets. These oppositely charged ions effectively neutralize the charge on the sheet.
Some typical corona generators, albeit not for static elimination but rather for charging purposes, are shown in U.S. Pat. Nos. 3,457,405; 3,566,223; 3,908,127 and 3,936,635. As can be seen in these patents, the end supports for the corona wires to position and tension the wires are relatively complex in either the shape or number of the parts employed. Furthermore a multiplicity of elements are required to electrically couple the high voltage source to the corona wire.